The present invention relates to a pneumatic radial ply tire, more particularly a radial ply tire and, in particular, a radial tire suitable for use for the truck, bus, light truck and other vehicles, and is intended for providing an improved radial tire, in which various requirement for this kind of tire as resistance to cutting resistance to wear, durability to high speed running, low fuel consumption, and vehicle driving stability are well-balanced with each other and also with general characteristics indispensable for the tire such as comfortableness in vehicle riding and traction capacity without affecting these characteristics, while optimizing a radius of curvature of the shoulder part of the carcass line, mainly based a new knowledge about a radial profile of the carcass line of radial tires.
The main points of the prior art for achieving improvement in resistance of tire to wear and cutting, and saving of fuel consumption have been such means as the use of rubber highly resistant to wear and cutting for the grounding part of said tread, preparation of rubber material high in repulsive resilience.
The reduction of durability of the tire to high speed running and saving of fuel consumption due to use of the rubber compound with high resistance to cutting and wear, was made up compensate by such means that the tread was radially divided into two parts of cap tread and base tread and the rubber compound with high resistance to cutting and wear is used for the cap tread and the rubber compound with low hysteresis loss is used for the base tread.
By the use of the said counterplan, the improvement can be reached to the same extent. However, there has been a deficit that the effect of the early stage is extremely lowered from the middle use which the cap tread worn down, at the same time, the stiffness of tread region is reduced, so there have been such disadvantages as to be forced to induce the reduction of vehicle driving stability and traction capacity which are indispensable and fundamental performance for the pneumatic tires. On the other hand, owing to the use of the rubber compound with high repulsive resilience, the fuel consumption is improved but there is a problem that the traction capacity, especially the wet grip performance is reduced.